Supporting Idle Stations in Wireless Distribution Systems

ABSTRACT

One embodiment described herein, a method of supporting wireless stations in a wireless distribution system having a portal and one or more access points is described. The method comprises accepting by a first access point (AP) a set of filters from a station; receiving by the first AP signaling that the station enters into an idle mode and signaling the same to a server in the wireless distribution system; forwarding by the first AP the set of filters to the server, the set of filters being applied to messages directed to the station received by the server in the wireless distribution system; receiving a buffered message for the station from the server in response to the buffered message matching at least one of the set of filters; and forwarding the buffered message to the station in response to receiving the buffered message from the server.

RELATED APPLICATIONS

The present application claims priority from U.S. Application No.11/830,752 (Attorney Docket No. 6259P032), filed on 07 Jul. 2007, nowU.S. Pat. No. ______, the entire contents of which are incorporated byreference herein.

BACKGROUND OF THE INVENTION

The present invention pertains to wireless local area networks (WLANs),and more particularly, to methods of supporting idle stations in WLANsand wireless distribution systems (DS) operating under IEEE 802.11standards.

In wireless local area networks, such as networks using the 802.11model, consist of stations (STA) which are associated with access points(APs), which are in turn connected to a distribution system (DS). Itshould be noted that the DS is an abstract concept, and is notrestricted to a particular implementation or technology.

FIG. 1 shows a wireless DS connected to a wired network as known to theart. DS 100 connects to wired network 200 through portal 110. Accesspoints, 112, 114, 116, 118 provide wireless access to stations 120, 122,124. As is known to the art, when a station associates with an AP, theDS is notified of this event so that incoming packets destined for thestation are routed to the proper AP for delivery.

When a station is associated with an AP, such as station 124 associatedwith AP 116, implicit information is exchanged in order to keep theassociation state alive at both ends. For example, a STA may indicate tothe AP that it is either going into power-save state or out of it byeither setting bits in regular messages it sends to the AP or by sendinga NULL data frame (a data frame with no payload) with bits in the headerindicating change of state. The AP may set specific bits in the TIM(traffic indication map) information element in its beacons informingstations in power-save state that there may be packets buffered for themat the AP. Even though no explicit keepalive messages are exchanged,there is an expectation that an active connection be maintained by thestation at all times.

In draft submission, document IEEE 802.11-07/2169r0 to the IEEE P802.11group titled “Traffic Filtering and Sleep mode” on wireless LANs(incorporated herein by reference), a set of protocols and messages forsupporting traffic filtering and idle mode is proposed.

While the draft defines messages and behavior, it does not specifyimplementation details. Under the proposal, a station associated with anAP may specify filter parameters indicating what traffic it wishes toaccept. When the station goes into sleep mode, it is no longerassociated with a particular AP. The station is paged when trafficpassing the pre-established filter criteria is met. When the stationwakes from the sleep state, it reassociates with an AP.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be best understood by referring to the followingdescription and accompanying drawings that are used to illustrateembodiments of the invention.

FIG. 1. shows a block diagram of a wireless distribution system (DS) asknown to the art;

FIG. 2 shows a block diagram of a DS including a paging server; and

FIG. 3 shows a second block diagram of a DS including a paging server.

DETAILED DESCRIPTION

Embodiments of the invention relate to a distribution system (DS) in awireless IEEE 802.11 data network. In an embodiment of the invention, asshown in FIG. 2, sleep mode server 130 appears to DS 100 as anotheraccess point (AP). In operation, when a station such as station 124 goesinto idle mode, it is associated with server 130. Once this associationis made, DS 100 will direct traffic destined for station 124 to server130. Server 130 buffers this traffic and initiates the process of pagingstation 124 by all APs within the DS. When station 124 exits idle modeand reassociates with DS 100, for example through AP 116, server 130 isnotified of this event and sends the buffered traffic to station 124through its associated AP.

Battery life is an important consideration in portable devices. Aprimary means of increasing battery life in a portable device is toreduce the power used by the device. One approach to reducing power,particularly in digital devices, is to use idle or sleep modes, whereinmajor portions of the device are operated in low power modes, ordisabled completely.

Such reduced power modes introduce additional complexity, however, intowireless devices. In accordance with IEEE 802.11 wireless networkingstandards, once a station (STA) is associated with an access point (AP)which provides wireless services to that station, a fairly constantexchange of messages between AP and station continues, performing taskssuch as synchronization. For wireless stations, listening for, andresponding to these messages consumes power.

The IEEE 802.11 standard defines optional power save modes in which thestation signals to the AP it is associated with that it wishes to entera sleep state. If the AP supports sleep states, the AP acknowledges therequest, and begins buffering packets for the station. This allows thestation to reduce power to its wireless circuitry, while stillmaintaining an association with a specific AP. The AP still sends outregular beacon transmissions; if an AP has packets buffered for asleeping station, it indicates this in the beacon transmissions.Sleeping stations wake periodically and check these beacon transmissionsto see if the AP has packets waiting for it. If there are packetswaiting, the station exits sleep mode, and retrieves the packets. Thepackets may require further activity, such as accepting an incoming VOIPcall, or if no further activity is required, the station may transitionback to sleep mode. Note that during this sleep mode, the station isstill associated with an AP.

Buffering packets for sleeping clients is an expensive task for APs,requiring large buffers and complex management strategies.

Revisions to the 802.11 standard, such as those contemplated in thereferenced proposal, include the addition of an “idle mode” where astation is not required to maintain an active association with aspecific AP in the DS while it is in the idle mode. It is contemplatedthat this new “idle mode” will result in more power savings, since thestation is no longer associated with a particular AP. The proposal alsospecifies messages and behavior for the station to specify a set oftraffic filters, indicating what traffic the station wishes to benotified of. The proposal is also quiet on how these are to beimplemented.

According to the present invention, a sleep mode server 130 isestablished for DS 100. Stations 120, 122, 124 associate with APs whichare part of the DS. In the example of FIG. 2, station 124 is associatedwith AP 116. In accordance with the present invention, when station 124associated with AP 116 establishes filters indicating the types oftraffic the station wishes to receive, AP 116 forwards these filters toserver 130. When station 124 enters idle mode, it is disassociated fromAP 116. AP 116 signals server 130 when station 124 enters idle mode.Server 130 then signals DS 100 that station 124 is associated with it,with server 130.

Once associated with server 130, all traffic destined for station 124goes to server 130. When packets arrive at server 130 for idle station124, server 130 applies the previously set filters. When a packetsatisfying the filter criteria for station 124 is met, server 130 pagesstation 124 through all APs defined for DS 100. When station 124 exitsidle mode on decoding a page, it reassociates with an AP, for example AP116. This reassociation is broadcast to all APs in DS 100, whichincludes server 130. When server 130 receives this reassociationinformation it then forwards saved packets for station 124 to thestation's current AP, now AP 116.

It should be noted that while server 130 may functionally resemble an APin DS 100, it does not transmit or receive wireless traffic. Rather, itstores filter settings and buffers traffic for idle stations which havebeen associated with it, initiates paging for idle stations through allAPs associated with the DS, and forwards buffered frames to thosestations when they exit the idle state and reassociate with an AP in theDS.

FIG. 3 shows a block diagram of a DS including a server according to anembodiment of the present invention. Portal 110 connects to wirednetwork through network interface 300. Access points 112, 114, 116, and118 also attach to portal 110. Portal 110 has CPU 310 and memoryhierarchy 320 which communicates 330 with network interface 300 andnetwork interfaces 340, 343, 344. Depending on the complexity of portal110, the communication 330 among CPU, memory, and network interfaces maybe simple interconnections and busses, or may be a more complexswitching fabric. Memory hierarchy 320 typically contains high speedread-write memory as well as nonvolatile memory such as flash. Memoryhierarchy 320 contains instructions and data which are executed orinterpreted by CPU 310 to perform the various tasks and processesdescribed herein. CPU 310 may be any suitable processor, such as thosein the PowerPC, MIPS, or IA86 families.

Network interfaces 300, 340, 343, 344 are typically Ethernet interfaces,with interfaces 340, 342, 344 optionally supporting IEEE 802.3 Powerover Ethernet (PoE) standards such as 802.3af and 802.3at to providepower to APs 112, 114, 116, 118.

Access points (APs) 112, 114, 116, 118 are shown in a block diagram asrepresentative AP 116. Network interface 400 connects to CPU 410 andmemory hierarchy 420, and to radio 430. Radio 430 is typically a radiomodule designed for use with the 802.11a, b, g, or n standards. Suchradio modules are available from Atheros Communications, among others.An AP may contain one or more radio modules. As an example, separateradio modules may be used for 2.4 GHz 802.11b/g/n and 5 GHz 802.11a. CPU410 is typically a processor designed for embedded systems, such as amember of the MIPS family. Memory hierarchy 420 usually includes highspeed read-write memory such as DRAM, as well as non-volatile memorysuch as flash. Memory hierarchy 420 contains instructions and data whichare executed or interpreted by CPU 410 to perform the various processesand tasks described herein. In operation, an AP such as AP 116 may haveall the programming information, code and data, required already presentin memory 420. In other implementations an AP may only contain enoughprogramming information in memory 420 to start up the AP and downloadfurther programming information from portal 110. In a highly integratedAP, CPU 410, network interface 400, and much of the support logicrequired for memory hierarchy 420 and radio 430 may be integrated intoone or more complex integrated circuits, usually identified assystem-on-chip (SOC) design.

As is understood by the art, such embedded systems as APs 112, 114, 116,118 and portal 110 run under the control of an operating system such asone of the many Linux family of systems, or a proprietary system such asVxWorks.

According to an embodiment of the present invention, server 130 is afunction of DS 100. Since server 130 does not require the ability tohandle radio traffic directly, server 130 may be implemented as aprocess running in DS 100, as an example, in portal 110. While pagingserver 130 may be run as a process in an AP such as AP 112, or 114, APsare usually more resource-limited than controllers, with controller 110most likely containing more memory and a faster processor than thoseused in the attached APs. Paging server 130 may also be hosted onseparate hardware, such as a repurposed AP. In one embodiment, such arepurposed AP need not contain radios 430, and may contain additionalread-write memory in memory hierarchy 420 to support additionalbuffering of traffic for idle stations.

In an embodiment such as that shown in FIG. 3, portal 110 controls aplurality of APs, which may represent one or more distribution systems(DS). Similarly, portal 110 may host multiple instances of server 130,one for each DS it serves.

While the invention has been described in terms of several embodiments,the invention should not be limited to only those embodiments described,but can be practiced with modification and alteration within the spiritand scope of the appended claims. The description is this to be regardedas illustrative rather than limiting.

1. A method of supporting wireless stations in a wireless distributionsystem having a portal and one or more access points comprising:accepting by a first access point (AP) a set of filters from a stationassociated with the first AP; receiving by the first AP signaling thatthe station enters into an idle mode; signaling by the first AP to aserver in the wireless distribution system that the station enters intothe idle mode; forwarding by the first AP the set of filters to theserver, the set of filters being applied to messages directed to thestation received by the server in the wireless distribution system;receiving a buffered message for the station from the server in responseto the buffered message matching at least one of the set of filters; andforwarding the buffered message to the station in response to receivingthe buffered message from the server.
 2. The method of claim 1, whereinthe buffered message is forwarded to the station in response to a secondAP in the wireless distribution system receiving an association requestfrom the client.
 3. The method of claim 2, wherein the server comprisesa process running on one of: (i) an AP in the distribution system; and,(ii) the portal.
 4. The method of claim 1, wherein the server comprisesa standalone device having no capability of transmitting or receivingwireless traffic.
 5. The method of claim 1, further comprising:receiving by the first AP a re-association request from the station;broadcasting by the first AP the re-association request from the stationin the wireless distribution system; and receiving the buffered messagefor the station from the server in response to broadcasting there-association request.
 6. The method of claim 1, wherein the set offilters are applied to messages directed to the station received by theserver through a plurality of APs in the wireless distribution system.7. A network device for supporting wireless stations in a wirelessdistribution system having a portal and one or more access pointscomprising: a memory; a processor; an accepting mechanism operating withthe processor, the accepting mechanism to accept a set of filters from astation associated with the first AP; a receiving mechanism operatingwith the processor, the receiving mechanism to receive signaling thatthe station enters into an idle mode, wherein the receiving mechanismfurther to receive a buffered message for the station from the server inresponse to the buffered message matching at least one of the set offilters; a signaling mechanism operating with the processor, thesignaling mechanism to signal to a server in the wireless distributionsystem that the station enters into the idle mode; a forwardingmechanism operating with the processor, the forwarding mechanism toforward the set of filters to the server, the set of filters beingapplied to messages directed to the station received by the server inthe wireless distribution system, wherein the forwarding mechanismfurther to forward the buffered message to the station in response tothe receiving mechanism receives the buffered message from the server.8. The network device of claim 7, wherein the buffered message isforwarded to the station in response to a second AP in the wirelessdistribution system receiving an association request from the client. 9.The network device of claim 8, wherein the server comprises a processrunning on one of: (i) an AP in the distribution system; and, (ii) theportal.
 10. The network device of claim 7, wherein the server comprisesa standalone device having no capability of transmitting or receivingwireless traffic.
 11. The network device of claim 7, further comprising:a broadcasting mechanism operating with the processor, the broadcastingmechanism to broadcast a re-association request from the station in thewireless distribution system; wherein the receiving mechanism further toreceive a re-association request from the station; and wherein thereceiving mechanism further to receive the buffered message for thestation from the server in response to the broadcasting mechanismbroadcasts the re-association request.
 12. The network device of claim7, wherein the set of filters are applied to messages directed to thestation received by the server through a plurality of APs in thewireless distribution system.
 13. A non-transitory computer readablemedium, implemented within an access point (AP) within a wirelessdistribution system including a portal and a plurality of access points,having a set of instructions stored therein, which when executed cause aset of operations to be performed, comprising: accepting a set offilters from a station associated with a first AP; receiving signalingthat the station enters into an idle mode; signaling to a server in thewireless distribution system that the station enters into the idle mode;forwarding the set of filters to the server, the set of filters beingapplied to messages directed to the station received by the server inthe wireless distribution system; receiving a buffered message for thestation from the server in response to the buffered message matching atleast one of the set of filters; and forwarding the buffered message tothe station in response to receiving the buffered message from theserver.
 14. The non-transitory computer readable medium of claim 13,wherein the buffered message is forwarded to the station in response toa second AP in the wireless distribution system receiving an associationrequest from the client.
 15. The non-transitory computer readable mediumof claim 14, wherein the server comprises a process running on one of:(i) an AP in the distribution system; and, (ii) the portal.
 16. Thenon-transitory computer readable medium of claim 13, wherein the servercomprises a standalone device having no capability of transmitting orreceiving wireless traffic.
 17. The non-transitory computer readablemedium of claim 13, wherein the set of instructions further comprises:receiving a re-association request from the station; broadcasting there-association request from the station in the wireless distributionsystem; and receiving the buffered message for the station from theserver in response to broadcasting the re-association request.
 18. Thenon-transitory computer readable medium of claim 13, wherein the set offilters are applied to messages directed to the station received by theserver through a plurality of APs in the wireless distribution system.19. A method of supporting wireless stations in a wireless distributionsystem having a portal for connectivity to a wired network and at leastone access point (AP), the method comprising: establishing a server inthe wireless distribution system to store information for one or morestations operating in an idle mode, wherein the server is capable oftransmitting or receiving wired traffic from the at least one AP;receiving by the server a signal from a first AP in the wirelessdistribution system, the signaling identifying that a station hasentered into an idle mode and is disassociated from the first AP;storing messages destined for the station by the server in response toreceiving the signal; receiving a set of filters originated from thestation from the first AP; applying the set of filters to the messagesdestined for the station by the server; and paging the station to exitthe idle mode in the wireless distribution system in response to one ofthe messages matching at least one of the set of filters.
 20. The methodof claim 19, wherein paging the station is performed through one of aplurality of APs in the wireless distribution system and the server. 21.The method of claim 19, further comprising: receiving a broadcastmessage from a second AP over the wireless distribution system, thebroadcast message indicating that the station has exited the idle modeand is associated with the second AP; and forwarding the messagesdestined for the station to the second AP for one or more subsequenttransmission to the station.
 22. The method of claim 21, wherein thesecond AP is identical to the first AP, and wherein the broadcastmessage comprises a re-association request.
 23. A network device forsupporting wireless stations in a wireless distribution system having aportal for connectivity to a wired network and at least one access point(AP), the network device comprising: a memory; a processor; anestablishing mechanism operating with the processor, the establishingmechanism to establish a server in the wireless distribution system tostore information for one or more stations operating in an idle mode,wherein the server is capable of transmitting or receiving wired trafficfrom the at least one AP; a receiving mechanism operating with theprocessor, the receiving mechanism to receive a signal from a first APin the wireless distribution system, the signaling identifying that astation has entered into an idle mode and is disassociated from thefirst AP, wherein the receiving mechanism further to receive a set offilters originated from the station from the first AP; a storingmechanism operating with the memory, the storing mechanism to storemessages destined for the station by the server in response to receivingthe signal; a filtering mechanism operating with the processor, thefiltering mechanism to apply the set of filters to the messages destinedfor the station by the server; and a paging mechanism operating with theprocessor, the paging mechanism to page the station to exit the idlemode in the wireless distribution system in response to one of themessages matching at least one of the set of filters.
 24. The networkdevice of claim 23, wherein the paging mechanism pages the stationthrough one of a plurality of APs in the wireless distribution systemand the server.
 25. The network device of claim 23, wherein thereceiving mechanism further to receive a broadcast message from a secondAP over the wireless distribution system, the broadcast messageindicating that the station has exited the idle mode and is associatedwith the second AP; and wherein the network device further comprises aforwarding mechanism operating with the processor, the forwardingmechanism to forward the messages destined for the station to the secondAP for one or more subsequent transmission to the station.
 26. Thenetwork of claim 25, wherein the second AP is identical to the first AP,and wherein the broadcast message comprises a re-association request.27. A non-transitory computer readable medium, implemented within anaccess point (AP) within a wireless distribution system including aportal and a plurality of access points, having a set of instructionsstored therein, which when executed cause a set of operations to beperformed, comprising: establishing a server in the wirelessdistribution system to store information for one or more stationsoperating in an idle mode, wherein the server is capable of transmittingor receiving wired traffic from the at least one AP; receiving a signalfrom a first AP in the wireless distribution system, the signalingidentifying that a station has entered into an idle mode and isdisassociated from the first AP; storing messages destined for thestation in response to receiving the signal; receiving a set of filtersoriginated from the station from the first AP; applying the set offilters to the messages destined for the station; and paging the stationto exit the idle mode in the wireless distribution system in response toone of the messages matching at least one of the set of filters